This invention relates in general to telemetry drill pipe, and in particular to drill pipe having a system that enables electrical signals to be passed through the sections of drill pipe to the surface.
Oil and gas wells are normally drilled with a string of drill pipe having a rotatable drill bit located on the bottom. The drill string is rotated to rotate the drill bit to disintegrate the earth formation. Drilling fluid or mud is pumped down the drill string to exit from the bit and return up the borehole. The drill string is made up of sections of pipe, each section being about 30 feet long and secured by threads to other sections to make up a string that is often thousands of feet long.
A method for determining certain downhole characteristics while drilling has long been needed. For example, it would be desirable to know the azimuth and angle of the hole while drilling. Many telemetry systems for drill pipe have been proposed. In many of the proposals, each drill pipe section has a segment of wire that extends its length. Electrical contacts are located at the ends of the wire segment. The contacts are adapted to make a connection automatically when the drill string is screwed together.
Although there are many proposals, these systems are not in general use because of complexity, and electrical leakage and continuity problems. The drill pipe itself is a conductor, and normally the drilling mud is a conductor. Consequently, the contacts must be located in insulators isolated from the metal of the drill pipe and from the mud. Still, due to the high pressure of the drilling fluid, electrical leakage may occur.
In a typical drill string, several hundred contacts must make good connection. These contacts must tightly fit with each other each time the sections of the drill string are connected together. Deposits on the contacts, such as dried drilling mud, may cause lack of continuity. It is not feasible for the drill rig personnel to wipe and clean the contacts during each trip.